The present invention relates to decanter centrifuges and, more particularly, to a decanter centrifuge which includes a gear box mounted to and spaced apart from a bowl.
Decanter centrifuges are well known in the art and are commonly utilized to separate a liquid feed mixture into its constituent parts. FIG. 1 illustrates a conventional decanter centrifuge. The decanter centrifuge includes a rotating bowl 2 typically having a cylindrical portion and a frustoconical end portion. The bowl 2 is engaged to a first drive motor M1 which is generally fixed to a support or base. The first drive motor M1 rotates the bowl 2 about its longitudinal axis.
A screw conveyor 4 is rotatably disposed within the bowl 2 and includes one or more spiraled flights 5. The screw conveyor 4 is engaged with a differential box 6 which drives the screw conveyor 4 at a differential speed with respect to the bowl 2. A second motor M2 is engaged with the differential box 6 for driving the screw conveyor 4.
In operation, a liquid feed mixture or slurry is fed into the bowl 2. Rotation of the bowl 2 generates a centrifugal force on the liquid feed which separates the feed into an effluent portion and a solids portion. The terms xe2x80x9clight phasexe2x80x9d and xe2x80x9cheavy phasexe2x80x9d are sometimes employed to refer to these constituent parts. The light phase is a liquid and the heavy phase is a concentrated solids material.
The screw conveyor 4 is rotated inside the bowl by the differential box 6, usually a gear box, at a differential speed with respect to the bowl 2. As such, the flights 5 on the screw conveyor 4 push the separated heavy phase towards the conical end of the bowl 2. One or more solids discharge ports 7 are formed in the bowl 2 for discharging the heavy phase. The light phase is discharged from the bowl 2 through one or more effluent discharge ports 8, typically located at the opposite end of the bowl from the solids discharge.
As shown in FIG. 1, the bowl 2 is attached to the first drive motor M1 and the gear box 6 through hubs. The hubs extend through pillow block bearings 9 which rotatably support the bowl. A conveyor shaft extends from both ends of the screw conveyor 4. The conveyor shaft is engaged with the gear box 6. The pillow block bearings support the bowl and the screw conveyor 4.
As illustrated, both motors, as well as the gear box, are mounted outboard of the pillow block bearings. This type of conventional mounting arrangement for decanter centrifuges is generally adequate when the gear box is relatively small in comparison to the bowl size. In certain applications, however, such as with municipal waste, it is necessary to create a relatively dry heavy phase. In such applications, additional torque is needed to rotate the conveyor. This necessitates an increase in the size and weight of the gear box 6. However, increasing the size and weight of the gear box leads to strength problems with the hub 3 and lowers the natural frequency of the decanter centrifuge.
Also, the pillow block bearings in a conventional decanter are typically operating above their manufacturer-rated speed. To reduce the speed of the bearings closer to the catalog rating, it would be necessary to reduce the size of the bearing which, in turn, would require a reduction in the size of the hub 3 passing through the bearing. However, in order for the gear box to provide increased torque, the hub 3 must be large enough to transmit the torque, support the gear box, and prevent the natural frequency of the gear box on the hub from being near the bowl""s operating speed. Thus, to date, the design of conventional decanter centrifuges usually involves a compromise which limits the use of the centrifuges.
The present invention is directed toward a decanter centrifuge for separating a liquid feed mixture into constituent parts. The decanter centrifuge includes a bowl assembly comprising a bowl mounted for rotation about a longitudinal axis and a differential box. The bowl assembly has first and second hubs located at its opposite ends. First and second bearings are also located on opposite ends of the bowl assembly. The first bearing rotatably supports the first hub and the second bearing rotatably supports the second hub. A first drive motor is engaged with the first hub for rotating the bowl about the longitudinal axis.
A screw conveyor is coaxially mounted within the bowl and has an attached conveyor shaft. The conveyor shaft is engaged with a differential box, often a gear box, located between the second bearing and the bowl (in this application, differential box and gear box will be used interchangeably). The gear box is adapted to rotate the conveyor shaft at a relative speed with respect to the bowl. A second motor, electrical brake, or torque arm is preferably engaged to the input shaft of the gear box.
The gear box is attached to the bowl by means of a plurality of circumferentially spaced posts. The posts fixedly position the gear box in a spaced relationship with the bowl. The space between the gear box and the bowl is preferably sufficient to minimize or prevent effluent being discharged from the bowl from washing against the gear box, and be large enough to allow an operator to change effluent dams.
The foregoing and other features and advantages of the present invention will become more apparent in light of the following detailed description of the preferred embodiments thereof, as illustrated in the accompanying figures.